FIG. 1 shows a mobile communications network 10. A base station 12 is positioned in a covered area or cell 16. Mobile terminals (e.g., cell phones) 14 in the vicinity of cell 16 are capable of communicating with other mobile terminals 14 or 14' or stationary terminals 26. This invention is illustrated herein with reference to a cellular communications system, although, the invention is applicable to any communications system in which terminals or transceivers are mobile, move from cell to cell, and register and deregister with base stations as a result of movement from cell to cell. To communicate with such other terminals 14, 14' or 26, the mobile terminals 14 communicate (transmit and receive) signals and messages with the base station 12. Mobile terminal 14' is outside of the cell 16 and does not use the base station 12 for purposes of communicating with other terminals 14 or 26. However, the mobile terminal 14' may be in another cell (not shown) serviced by another base station (not shown) which provides service to the mobile terminal 14' in an analogous fashion as described below.
By their nature, mobile terminals 14 and 14' are mobile. It is important to keep track of the location of mobile terminals 14 or 14' (i.e., in which cells 16 they are located) in order to enable the mobile terminals to originate calls, to receive calls and to maintain calls, despite any dynamic movement of the mobile terminals 14 or 14'. To that end, home location registers (HLRs) 22 and visitor location registers (VLRs) 20 are provided. The purpose of the HLR 22 is to keep track of a specific, predetermined group of mobile terminals 14, 14', wherever they may move, and to provide telephone number to routing address mapping. The purpose of the VLR 20 is to keep track of any mobile terminals 14 which move into a specific registration area (RA) managed by the VLR 20. For sake of convenience herein, it is assumed that the RA covers the same geography as the cell 16, although it is possible for the RA to cover a different sized area than the cell 16 (e.g., the RA can cover multiple cells 16). Stated one way, the HLR 22 is a mobile terminal specific register, whereas the VLR 20 is a location specific register.
According to the GSM and IS-41 standards, mobile terminals 14, 14' VLRs 20 and HLRs 22 obey a handoff registration procedure in order to keep track of the mobile terminals 14, 14'. Generally stated, a mobile terminal 14, 14' registers with a VLR 20 when it moves into the RA of the VLR 20 and deregisters with the VLR of the RA out of which the mobile terminal 14, 14' has moved. The VLR 20 with which the mobile terminal 14,14' registers records information regarding the mobile terminal 14, 14' in a local database. The VLR 20 also contacts the HLR 22 and informs the HLR 22 that a mobile terminal 14,14' of which the HLR 22 keeps track has now moved into the RA covered by the VLR 20. FIG. 2 shows an illustrative architecture for the VLR 20 or HLR 22. The VLR 20 or HLR 22 has a processor 31, main memory 33, disk memory 35, receiver 37 and transmitter 39 connected to a bus 30. (The receiver 37 and transmitter 39 may be combined into a single transceiver.)
When another terminal, such as stationary terminal 26, desires to contact the mobile terminal 14, 14' , the public switched telephone network (PSTN) 24 contacts the HLR 22. The HLR 22 obtains the appropriate routing information from the VLR 20 covering the RA in which the mobile terminal 14 is located. The HLR 22 then routes the call, using routing information provided by the VLR 20, and via the mobile switching center (MSC) 18 and base station 12, to the mobile terminal 14. Likewise, when the mobile terminal 14 desires to originate a call, the base station 12 routes the originating call to the MSC 18. The MSC 18 contacts the VLR 20 that covers the RA in which the mobile terminal 14 is located. The VLR 20 provides the necessary routing information to the MSC 18 which then completes the call, e.g., using the PSTN 24.
These registration and call origination/completion procedures are now described in greater detail. In the illustrations below, it is assumed that all actions of the VLR V2 20 or HLR 22 are performed under control of the processor 31 (FIG. 2) located at the VLR 20 or HLR 22, respectively. Likewise, all messages are presumed to be received by the appropriate receiver 37 or transmitted by the appropriate transmitter 39. Records are stored, retrieved or modified in a storage that includes the disk memory 35 and/or main memory 33. Note also that the process steps described below are abbreviated for sake of clarity. For example, security steps have been omitted.
FIG. 3 shows the registration operation:
S1.1 In a first step S1.1, the mobile terminal u1 14 transmits a registration request message reg.sub.-- msg to the VLR V2 20 that covers the RA into which the mobile terminal u1 14 has moved. PA1 S1.2 Next, in step S1.2, the VLR V2 20 sets up a temporary user record u1 in its storage. PA1 S1.3 In step S1.3, the VLR V2 20 transmits the message reg.sub.-- jmsg(u1) to the HLR which message indicates the registration of the mobile terminal u1 at the VLR V2 20. The message reg.sub.-- msg(u1) is the MAP.sub.-- UPDATE.sub.-- LOCATION message according to the GSM standard and the message REGNOT in according to the IS-41 standard. PA1 S2.1 The HLR 22 receives the message reg.sub.-- msg(u1). In step S2.1, the HLR 20 updates the map record corresponding to mobile terminal u1 14. That is, u1 is used as an index to retrieve the map record corresponding thereto. The indication of the retrieved map record that indicates the VLR covering the RA into which the mobile terminal u1 14 has moved is modified to indicate the VLR V2 20. PA1 S2.2 In step S2.2, the HLR 22 transmits a message reg.sub.-- ack(u1,profile) to the VLR V2 20 which transmitted the reg.sub.-- msg(u1) to the HLR 20 in step S1.3. This message acknowledges receipt of the message reg.sub.-- msg(u1) and the updating of the map record at the HLR 22. The reg.sub.-- ack is the MAP.sub.-- UPDATE.sub.-- LOCATION.sub.-- ack message according to the GSM standard and the message regnot according to the IS-41 standard. PA1 S2.3 VLR V2 20 receives the message reg.sub.-- ack(u1,profile) message and finalizes the user record for mobile terminal u1 14. In step S2.3, VLR V2 20 transmits the message reg.sub.-- ack to the mobile terminal u1 14 acknowledging completion of the registration process. PA1 S3.1 In step S3.1, the HLR 22 first transmits the message cancel.sub.-- msg(u1) to the VLR V1 covering the RA from which the mobile terminal u1 14 has moved. This message requests that the VLR V1 cancel its user record for the mobile terminal u1. The cancel.sub.-- msg message is the MAP.sub.-- CANCEL.sub.-- LOCATION message according to the GSM standard and the REGCANC message according to the IS-41 standard. PA1 S3.2 In step S3.2, VLR V1 20 deletes the user record for the mobile terminal u1 14. PA1 S3.3 In step S3.3, VLR V1 20 transmits the message cancel.sub.-- ack to the HLR 22 in order to acknowledge cancellation of the user record. The cancel.sub.-- ack message is the MAP.sub.-- CANCEL.sub.-- LOCATION.sub.-- ack message according to the GSM standard and the regcanc message according to the IS-41 standard. PA1 S4.1 In step S4.1, the mobile terminal u1 transmits a message for originating a call to the MSC. PA1 S4.2 The MSC receives the call origination message. In step S4.2, the MSC transmits a call.sub.-- req(u1) message to the VLR V2 which message requests the VLR V2 to approve or disapprove the call request. The call.sub.-- req message is the MAP.sub.-- SEND.sub.-- INFO.sub.-- FOR.sub.-- OUTGOING.sub.-- CALL according to the GSM standard and ORREQ according to the IS-41 standard. PA1 S4.3 VLR V2 receives the call.sub.-- req(u1) message. In step S4.3, VLR V2 examines the user record for mobile terminal u1 and allows the request. VLR V2 transmits the message call.sub.-- ack to the MSC which message approves the call. The call acknowledge message is the MAP.sub.-- SEND.sub.-- INFO.sub.-- FOR.sub.-- OUTGOING.sub.-- CALL.sub.-- ack message according to the GSM standard and the orreq message according to the IS-41 standard. PA1 S4.4 In step S4.4, the MSC completes the call. In this case, the called terminal is the stationary terminal 26. Therefore, the call is completed through the PSTN 24. PA1 S5.1 In step S5.1, the originating terminal 26 dials the mobile terminal's u1 phone number, which illustratively is the mobile subscriber ISDN number (MSISDN) according to the GSM standard and the mobile identification number (MIN) according to the IS-41 standard. PA1 S5.2 In step S5.2, a central office or toll office switch of the PSTN 24 transmits the message loc.sub.-- req(u1) to the HLR of the mobile terminal u1. The message loc.sub.-- req(u1) requests the routing address for the mobile terminal u1. The loc.sub.-- req message is the MAP.sub.-- SEND.sub.-- ROUTING.sub.-- INFORMATION message according to the GSM standard and the ROUTREQ message according to the IS-41 standard. PA1 S5.3 In step S5.3, HLR examines the map record indexed by the mobile terminal u1 identifier. The retrieved map record indicates that the mobile terminal is in the RA covered by VLR V2. The HLR thus transmits the message rout.sub.-- req(u1) to VLR V2 to determine the routing information for mobile terminal u1. The rout.sub.-- req message is the MAP.sub.-- PROVIDE.sub.-- ROAMING.sub.-- NUMBER message according to the GSM standard and the ROUTREQ message according to the IS-41 standard. PA1 S5.4 The message rout.sub.-- req(u1) is received at VLR V2. In step S5.4, VLR V2 determines the routing address of mobile terminal u1. VLR V2 then transmits the message rout.sub.-- ack(rout.sub.-- addr) back to the HLR of mobile terminal u1 containing the routing address "rout.sub.-- addr" for the mobile terminal u1. The message rout.sub.-- ack is the MAP.sub.-- PROVIDE.sub.-- ROAMING.sub.-- NUMBER.sub.-- ack message according to the GSM standard and routreq according to the IS-41 standard. PA1 S5.5 The HLR receives the message rout.sub.-- ack(rout.sub.-- addr). In step S5.5, the HLR transmits the message loc.sub.-- ack(rout.sub.-- addr) to the switch of PSTN 24 which originally transmitted the message loc.sub.-- req(u1), which message contains the requested routing address for the mobile terminal u1. The message loc.sub.-- ack is the MAP.sub.-- SEND.sub.-- ROUTING.sub.-- INFORMATION.sub.-- ack according to the GSM standard and routreq according to the IS-41 standard. PA1 S5.6 In step S5.6, the switch of PSTN 24 that receives the message loc.sub.-- ack(rout.sub.-- addr) uses the routing address rout.sub.-- addr for connecting the call to MSC. PA1 S5.7 In step S5.7, MSC pages the mobile terminal u1 within its coverage area and connects the call to mobile terminal u1 after receiving an acknowledgment from mobile terminal u1.
FIG. 4 shows a conventional registration cancellation (deregistration) process in which the mobile terminal u1 14 moves from the RA of VLR V1 20 to the RA of VLR V2 20:
FIG. 5 shows a conventional call origination process:
FIG. 6 shows the call termination (completion) process. In this illustration, the call is assumed to have originated from the stationary terminal 26 on the PSTN 24:
Generally speaking, the HLR can be designed to always have sufficient storage space for storing enough records to keep track of each mobile terminal to which it is assigned. On the other hand, the VLR cannot be guaranteed to have sufficient storage space to maintain user records for every mobile terminal that might move into the RA covered by the VLR. If the VLR runs out of storage space for user records then a mobile terminal moving into the RA covered by the VLR is refused service. This is disadvantageous.
It is an object of the present invention to overcome the disadvantages of the prior art.